Thermostatic overload relay



Oct. 16, 1951 G. c. ARMSTRONG ETAL 2,571,812

THERMOSTATIC OVERLOAD RELAY Filed Nov. 1, 1949 Fig.l

l5 l4 l6 (ID 1 KID l 31 30 4| Fig.2

l I I l INVENTORS George G. Armstrong,

Robert T. Busnelt 8 Delbert Ellis. BY

ATT RNE Patented Oct. 16, 1 951 THERMOSTATIC OVERLOAD RELAY George G. Armstrong, Buflalo, and Robert T. Basnett, Kenmore, N. Y., and Delbert Ellis, Beaver, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application November 1, 1949, Serial No. 124,742

11 Claims. 1

Our invention relates to thermostatic overload relays for the protection of electric circuits or devices as known, for instance, from Patent 2,- 195,012 of L. Pierce and Patent 2,414,513 of D. Ellis and O. L. Taylor.

It is among the more general objects of our invention to improve such relays as regards simplicity of design and manufacture and facility of selective adjustment as compared with relays according to the above-mentioned patents.

A more specific object of the invention is to devise an overload relay whose thermostatically controllable switching device, including a pivoted switch arm with a biasin spring and a manually operable reset or control plunger also with a biasing spring, are secured to the insulating body of the relay by a single fastening member so that all these parts are held in proper relation to one another when the one fastening member is attached, or can all be separated from the relay when the fastenin member is removed.

Another object of the invention is to improve the insulation and simplify the design of the switch arm and appertaining movable contact of an overload relay.

Still another object of the invention is to make an overload relay more readily adjustable for automatic or manual closing of the relay contacts than the known relays and to permit a selective setting of the relay for only automatic opening or for automatic and manual opening. More specifically, the invention aims at permittin these selective adjustments simply by correspondingly displacing a readily accessible adjustin member without disassembl or removal of any relay part.

These and other objects, as well as the means provided by the invention for achieving them, will be apparent from the following description of the embodiment exemplified on the drawing in which:

Figure l is a top view of a relay according to the invention, Figure 2 is a side view of the same relay, and Figur 3 a view from the opposite side of the relay.

Figure 4 is a sectional view, the section being taken along the vertical plane denoted in Figure 3 by line IVIV.

Figure 5 is a part-sectional and perspective view of the same relay with an appertaining cover plate removed to show the interior.

Figure 6 is a front view of a switch arm with an appertaining contact bridge, and Figure 7 shows the same parts by a lateral view.

Figure 8 shows a cover plate and spring appertaining to the same relay.

The illustrated relay serves to protect an electric circuit or apparatus from damage due to overload by actuating an electric switch in response to the heat developed by an overloadresponsive heater. The switch, in turn, controls a contactor or the like devic for disconnecting the circuit or apparatus to be protected. Only the overload-responsive relay unit proper is concerned by this invention while the separate circuits or apparatus controlled and protected thereby may be of any customary type and hence are not illustrated in the drawing.

The illustrated relay has a sheet-metal base plate I firmly attached to an insulating body 2, for instance, of molded material. The body 2 is traversed by a cavity 3 with a circular ledge or shoulder against which is seated a thermostatic assembly. This assembly is composed of a curved snap disc 4 of bimetal, a retaining ring 5, a cup 6, and a stud I such as a rivet or screw bolt. Ring 5 is secured in cup 6 by press fit. Cup 6 rests against the circular ledge of opening 3. When disc 4 is suiiiciently heated, its center can snap toward the left (Fig. 4) and move the head of stud 1 through somewhat wider center openings in the bottom of cup 6 toward a contact member still to be described. The cup-and-disc assembly is secured in base 5 with the aid of an annular spring member 9 of spring steel which has two diametrically opposite, radially projecting lugs ll, l2 that engage two corresponding projections of the insulating body 2, one of these projections being visible in Fig. 5 at l3. The lugs and projections form together a lock which permits introducing the cup-and-disc assembly and the spring 9 from the left of Fig. 4. when the spring is in one angular position and then fastening the assembly and sprin merely by applying pressure to the spring while turning it into locking position. Further details of this particular thermostatic assembly are not described in this specification because they ar more fully disclosed in the copending application, Serial No. 114,049, filed September 3, 1949, entitled Thermostatic Snap Disc Relays, of G. C. Armstrong, and are not essential to the present invention proper. Indeed, as far as the present invention is concerned, the described thermostat assembly can be replaced by those of other designs, for instance as shown in the above-mentioned Patents 2,195,012 and 2,414,513. For understanding the invention, it suffices to keep in mind that the bimetal disc of the thermostatic device will snap toward the left (Fig. 4) when sufiiciently heated due to overload current; when thereafter the device cools off, for instance due to the protective action initiated by the just-mentioned contact, the disc will return to its normal, illustrated position.

The disc is heated indirectly by a heater. R4 of resistance material which is attached to two terminals l5, I5. A loop portion of heater l4 lies in the cavity of the insulating body 2 close to the bimetal disc 5. The terminals [5, l5 are mounted on the insulating body 2. When usin the relay, the terminals [5 and [6 are connected in the circuit to be protected. Then, the load current flows through the heater 14 so that the heat produced by the heater and transmitted to the disc 4 is a measure of the current, and the disc will snap if this current exceeds given overload conditions. The heater is exchangeable for others of difierent rating to make the relay applicable for different rated load currents.

The switch to be actuated by the thermostatic assembly has two terminals 2| and 22 mounted on body 2 and integral with respective stationary contacts 23 and 24 which cooperate with a contact bridge 25 (Figs. 2 and 3). Contacts 23, 24 and bridge 25 are located within a cavity 26 in the bottom portion of insulating body 2. Bridge 25 is attached to a rigid arm 2'! of insulating material which has a bearing groove 28 (Fig. 5) engaged by an angularly bent nose 29 of a sheetmetal plate 3. Plate 3 is attached to body 2 by two screws 3|, 32. One of the holes in body 2 for the passage of the screws is visible in Fig. 5 at 33. Nose 29 and groove form together the pivot bearing for arm 27. A biasing spring 34 is disposed between the upper end of arm 2'5 and the body 2 and tends to keep arm 2'! and contact bridge 25 in the illustrated contact-closing posi tion. A spacing screw 35 is threaded through the arm 2'! and has its inner end engageable by the head of member 7. When, due to overload, the bimetal disc 4 snaps toward the left (Fig. 4), the head of stud 1 hits against the screw 35 and moves the arm clockwise (Fig. 4) about its pivot, thus moving the contact bridge 25 away from the stationary contacts 23 and 24. I

As a rule, the use of the relay is such that the just-mentioned movement of contact bridge 25 causes an interruption of the circuit for the electric heater element I4 so that the disc 4 is no longer heated. As soon as disc 4 has cooled to a predetermined lower temperature, it snaps back into the illustrated, normal position. A will be explained, the illustrated device can be selectively adjusted to three different settings. In one setting, the arm 21 is free to follow the bias of spring 34 and to reclose the circuit of contacts 23, 24, 25 when the disc 4 moves back to its normal position. In the other two settings, the arm 2'! is arrested in its contact-opening position so that, after the cooling and return movement of disc 4, a manual operation is necessary to make arm 21 reclose the relay contacts. The means for the selective adjustment and for the manual reclosing of the relay will be described presently.

A plunger 48 of insulating material is slidable in a groove of body 2 but not revolvable relative to the body. The upper portion of plunger 40, outside body 2, is shaped as a push button 4!. The groove for guiding the plunger 40 is open toward the plate 35, but the plunger is held in the groove when the plate 30 is attached. A wire spring 42 has a coiled portion loosely surrounding a boss43 (Fig. 3) of insulating material which is molded as an integral part of the insulating body 2. One end of spring 42 abuts at '30 to the body 2.

44 against an adjacent inner wall surface of body 2, while the other end of spring 42 passes through one of three notches 45, 46, 4? of plunger and at its extremity is bent to a loop 48 to facilitate setting the spring into a diiferent one of the three notches for the purpose explained below. Regardless of which of the three notches is engaged by the spring 42, the force of the spring acts upwardly on the plunger 49. When the plate 39 is removed, the spring 42 can be placed on the boss 44, and its proper position, like that of plunger 45 and arm 2'! with spring 34, is thereafter secured merely by fastening the plate The loop end 43 of spring 42 remains accessible after the relay is completely assembled, i. e., after plate is fastened to body 2. Then, the loop end 48 of spring 42 can be lifted toward the observer (Figs. 2, 5) and out of the previously occupied notch of the plunger and can be placed into any of the other two notches. The three selective settings are preferably identified by inscriptions on plate 36 reading, for instance, as shown in Fig. '7: Auto, Hand, and No Stop. These inscriptions correspond to the setting of the spring 42 into the top notch 45, the middle notch 45, and the bottom notch 41, respectively. The purposes and effects of these settings are as follows.

(1) When spring 42 is set in Auto position, i. e., engaged by the top notch 45 as illustrated in Fig. 5, the relay contacts will reset themselves automatically. That is, after the thermostatic device has responded to overload current and, by snapping of disc 4, has moved the arm 21 with contact bridge 25 into the open position, the arm 2! is free to return under the biasof spring 34 to the contact-closing position when thereafter the disc 4 cools off and snaps back to the normal position. This freedom of return'movement of arm 2'? is due to the fact that at this setting of spring 42, the plunger 40 is upwardly biased by spring 42 to a stop position in which the loop end 48 of spring 42 abuts against a projection 5| of plate 30 (Fig. 8). In this stop position, a groove of plunger 4!! lies behind a nose 52 (Figs. 2, 5) of arm 21, and this groove is deep enough to permit a free closing movement of nose 52 and arm 27. Also in the Auto position of spring 42, the push button 4| can be depressed by the operator at any time in order to open the relay contacts or to prevent them from reclosing. Such an actuation of push button 4! may serve to trip the main breaker or contactor (not shown) of a motor, thus permitting the operator to stop or jog the motor. When button 4! is being depressed, a bevel surface 53 (Figs. 2, 5) on plunger 40 engages a corresponding bevel face of the nose 52 and thus lifts the arm 2? with bridge 25 away from the stationary contacts 23 and 24.

(2) When the spring 42 is set in Hand position, i. e., engaged by the middle notch 46 (see Fig. 2), the relay after an overload-responsive opening of its contacts, will not reclose automatically but remains in contact-open condition until, after the cooling of disc 4, the push button 4| is depressed by the operator. This manually releasable locking comes about as follows. With spring 42 set in Hand position, the loop end 48 of spring 42 is'too far remote from the stop projection 5| (Fig. 2) of plate 30 to limit the upward movement of plunger 40. Consequently, the plunger moves a little farther upward until a stop projection 54 of the plunger abuts against the nose 52 of arm 27 (Fig. 2), assuming that arm 21 is in the contact-closed position. When thereafter,

due to overload response, the arm 2'! moves to the contact-open position, its nose 53 is lifted toward the observer (Fig. 2) and outof engagement with the stop projection 54 of plunger 40. The plunger, under the bias of spring 42, is now free to move upward a further extent until another stop pro- J'ection 55 of the plunger abuts against a stop face 56 of plate 30 (Fig. 2). In the position then reached by the plunger as, its other stop projection 54 lies behind the nose 52 of arm 2'! and prevents the arm from returning to the contactclosed position even after the thermostatic device has cooled and returned to its normal position. It is, therefore, necessary that the operator depress the button 4| for reclosing the relay contacts. During the downward movement of the plunger, the stop projection 54 slides below the nose 52 of arm 21 so that the arm is suddenly released to snap back to the closed-contact position. It is again possible to manually open the relay contacts, for instance, to stop a motor controlled by the relay. To this end, the operator has to depress the button 4| farther than just-mentioned until the bevel face 53 of plunger 40 engages and lifts th nose 52 of arm 21 as already described when explaining the Auto setting of the relay.

(3) When the spring 42 is set in No Stop position, i. e., when it engages the bottom notch of plunger 40, the operation is the same as with the above-described Hand setting except that now the relay contacts open only automatically in response to overload but cannot be manually opened by actuation of the push button. This is due to the fact that, with spring 42 set on No Stop, the loop end 48 lies close to a stop nose 51 (Figs. 2, 8) of plate 3|! and immediately abuts against this nose when an attempt is made to depress the button 4|. Thus the possible downward movement of the plunger is just large enough to permit a manually controlled reclosing of the relay contacts but is insuflicient to bring the bevel face 53 of plunger 40 into lifting engagement with nose 52 of arm 21.

The above-explained three settings of the relay permit adapting it to a variety of operating requirements. It will be recognized that a change in relay setting can be made with utmost facility without taking the relay apart and without removing any part therefrom.

It has been mentioned that the plate 30 with only two fastening screws holds all other relay parts together, aside from serving as a pivot and as a stop abutment for limiting the plunger travel. In addition, th plate 30 also cooperates in holding the contact bridge 25 attached to the arm 21 as will be presently set forth.

The contact bridge 25, according to the invention, is secured to the arm 2'! without the use of separate fastening means. To this end, the contact bridge 25 has a wider circular middle portion 6| with an elongated opening 61 as best apparent from Fig. 6, and the front end of the insulating arm 21 has a projecting stud 62 with two lateral lugs 63 and 64 at diagonally opposite sides of the stud. These lugs match the opening 61. Consequently, when the arm 2'! is removed from the relay, for instance, before the individual parts of the relay are assembled, the contact bridge 25 can be placed in the position indicated in Fig. 6 by a broken line 25', in which its opening 61 slides easily over the lugs 63 and 64. When the contact bridge is then turned into the normal position shown in full lines (Fig. 6), the lugs 63 and 64 of stud B2 catch over the central portion 6| of the bridge 25 and hold it in position; The body of the insulating arm 21 has ridges 65 and 66 (Figs. 6, 7) whose upper surfaces in the representation of Fig. 7 are vertically spaced from the lower surfaces of the lugs 63 and 64 by somewhat less than the thickness of the contact bridge 25. Consequently, when the contact bridge is placed on the stud 62 and turned from the position 25 to the normal position (Fig. 6), the bridge material is put under bending stress. Due to the elasticity of the material, the bridge 25 then exerts a force between the lugs 63, 64 and the ridges 65, 66 which is just sufiicient to produce a retaining friction without preventing a change in the angular position of the contact bridge relative to the arm 21 when sufiicient force is applied to the bridge. As a result, the bridge 25 is securely held in proper position after it is assembled with the arm 21, and both can then be placed as a unit into the cavity of the insulating body 2 when the relay is being assembled. When switch arm 2'! and plunger 49 with the appertaining biasing springs are at their proper places in the cavity of body 2, and when the front plate 30 is fastened to the body, the arm 2'! is limited in its angular movement about the pivot nose 29 to an extent sufficient for the desired operation of the relay but insufiicient to permit the contact bridge 25 from turning to the dotted line position (Fig. 6) in which. it could be accidentally removed from the arm 21. In this manner, the front plate 30 also secures the bridge 25 in proper position. Due to the force of the biasing spring 34 (Fig. 4), the bridge 25 automatically aligns itself to make simultaneous contact with the contact surfaces of the stationary contacts 23 and 24 and will automatically readjust itself if it should accidentally come out of alignment during the installation or use of the relay. Therefore, the above-described manner of design and attachment of the contact bridge is not only advantageous from the viewpoint of simplicity in design and assembly but affords also a better automatic aligning movement than possible in the above-mentioned known relays.

It will be apparent to those skilled in the art after a study of the present disclosure that relays according to the invention may be modified in various aspects, for instance, as regards the arrangement and shape of its described components without departin from the gist of the invention and within the scope of its essential features as set forth in the claims annexed hereto.

We claim as our invention:

1. A relay, comprising an insulating body having cavity open toward one side of said body, thermostat means mounted on said body and extending into said cavity, stationary contact means eng-ageable with said stationary contact movably disposed in said cavity and engageable by said thermostat means, said arm having an integral pivot element at its side facing the opening of said cavity and having movable contact means engageable with said stationary contact means, a biasin spring disposed in said cavity and engaging said arm, and a plate member attached to said body at said one side and extending over said cavity, said plate member having an integral pivot element engaging said arm pivot element so as to hold said arm and said spring in position.

2. A. relay, comprising an insulating body having thermostat means and having a cavity, stationary contact means mounted on said body, a pivotally movable insulatin arm disposed in said cavity and having movable contact means engageable with said stationary contact means, a spring disposed in said cavity in biasing engagement with said arm, said arm being engageable by said thermostat means to be moved thereby in opposition to said biasing spring, a plunger slidably disposed in said cavity and extending to the outside of said body, another biasin spring disposed in said cavity and engageable with said plunger for normally holding said plunger in a given position, said plunger being engageable with said arm for controlling the movement of said arm when said plunger is displaced from said position, and a fastening member attached to said body and extending over said cavity and over said plunger, said arm and said two springs and being the only means for securing plunger, arm and springs in proper relative relations within said cavity.

3. A relay, comprising an insulating body having thermostat means and having a cavity, stationary contact means mounted on said body, a pivotally movable insulating arm disposed in said cavity and having movable contact means engageable with said stationary contact means, a spring disposed in said cavity in biasing engagement with said arm, said arm being engageable by said thermostat means to be moved thereby in opposition to said biasing spring, a plunger slidably disposed in said cavity and extending to the outside of said body, another biasing spring disposed in said cavity and engageable with said plunger for normally holding said plunger in a given position, said plunger being engageable with said arm for controlling the movement of said arm when said plunger is displaced from said position, a plate member attached to said body over said cavity and extending over said plunger, said arm and said springs for securing them in proper relative positions within said cavity, said plate member having stop face means cooperatively related to said plunger to limit the displacement of said plunger.

4. A 'relay, comprising an insulating body having a cavity open toward one side of said body, thermostat means mounted on said body and extending into said cavity, stationary contact means mounted on said body, an insulating arm movably disposed in said cavity and engageable by said thermostat means, said arm having an integral pivot element at its side facing the opening of said cavity and having movable contact means engageable with said stationary contact means, a biasing spring disposed in said cavity and engaging said arm at its other side, a plate member attached to said body at said one side and extending over said cavity, said plate memher havin an integral pivot element engaging said arm pivot element so as to hold said arm and said spring in position, a plunger for manually operating said arm, said plunger having a projection and said plate member having a stop face engageable by said projection for limiting the displacement of said plunger.

5. A relay, comprising stationary contact means, a pivotally movable arm having movable contact means, a biasing spring engaging said arm for normally holding said movable contact means in contact with said stationary contact means, thermostat means engageable with said arm for automatically moving it to contact-open position, an axially slidable plunger biased toward a first position and manually movable to a second position and to a consecutive third position, said plunger and said arm having respective bevel faces engaging each other during displacement of said plunger from said second to said third position for manually moving said arm to contact-open position, said plunger and said arm having respective stop means engageable with each other when said plunger is in said second position to permit said plunger to slide from said second to said first position only when said arm is moved by said thermostat means to said contact-open position and to thereafter prevent said arm to return to contact-closed position, said plunger having a groove between said plunger bevel face and said plunger stop means to permit said arm to return from contact-open to contact-closed position when said plunger is in said second position, and selectively adjustable stop means engageable with said plunger and having three selective settings, said plunger being limited to displacements between first and second positions at one setting, between first and third positions at another setting, and between second and third positions at the third setting.

6. A relay, comprising stationary contact means, a pivotally movable arm having movable contact means, a biasing spring engaging said arm for normally holding said movable contact means in contact with said stationary contact means, thermostat means engageable with said arm for automatically moving it to contact-open position, an axially slidable plunger biased toward a first position and manually movable to a second position and to a consecutive third position, said plunger being in engagement with said arm when sliding from second to third position to then move said arm to contact-open position, said arm when in contact-closed position being engageable with said plunger to prevent. said plunger from sliding from second to first position, said plunger when in first position being in engagement with said armwhen said arm is in contact-open position to then prevent said arm from returning to contact-closed position, said arm and said plunger being mutually disengaged when said plunger is in second position, stationary stop means, and stop means selectively displaceable on said plunger and engageable with said stationary stop means for limiting the displacement of said plunger, said displaceable stop means having three selective settings relative to said plunger, said plunger being limited to 'displacements between first and second positions at one setting, between first and third positions at another setting, and between second and third positions at the third setting.

7. A relay, comprising stationary contact means, a pivotally movable arm having movable contact means, a biasing spring engaging said arm for normally holding said movable contact means in contact with said stationary contact means, thermostat means engageable with said arm for automatically moving it to contact-open position, an axially slidable plunger biased to ward a first position and manually movable to a second position and to consecutive third position, said plunger being in engagement with said arm when sliding from second to third position to then move said arm to contact-open position, said arm when in contact-closed position being engageable with said plunger to prevent said plunger from sliding from second to first position, said plunger when in first position being in engagement with said arm when said arm is in contact-open position to then prevent said arm from returning to contact-closed position, saidarm and said plunger being mutually disengaged when said plunger is in second position, stationary stop means, another biasing spring having an accessible end portion extending across said plunger said plunger having three axially spaced notches with which said end portion is selectively engageable for biasing said plunger toward said first position, said end portion being engageable with said stop means for limiting the displacement of said plunger in dependence upon the selected notch setting of said spring end portion, said plunger being limited to displacements between first and second positions at one setting, between first and third positions at another setting, and between second and third positions at the third setting.

8. A relay, comprising an insulating body having a cavity open toward one side of said body, thermostat means mounted on said body and extending into said cavity, stationary contact means mounted on said body, an insulating arm movably disposed in said cavity and engageable by said thermostat means, said arm having an integral pivot element at its side facing the opening of said cavity and having movable contact means engageable with said stationary contact means, a biasing spring disposed in said cavity and engaging said arm at its other side, a plunger axially displaceable in said cavity and extending to the outside of said body for manual actuation, a sprin disposed in said cavity and having an end portion, said plunger having a notch open toward said one side of said body and engaged by said end portion of said spring whereby said plunger is biased toward said outside, said plunger being engageable with said arm for controlling the movement of said arm depending upon the displacement position of said plunger, and a fastening member attached to said body and extending over said cavity and over said plunger, said arm and said two springs and being the only means for securing plunger, arm and springs in proper relative relations within said cavity.

9. In a relay according to claim 8, said insulating body having integral therewith a boss located within said cavity and extending close to said fastening member, said other spring having a coiled portion loosely seated on said boss and held in position by said fastening member.

10. A relay, comprising an insulating body having thermostat means and having a cavity, stationary contact means mounted on said body, a pivotally movable insulating arm disposed in said cavity and having movable contact means engageable with said stationary contact means, a spring disposed in said cavity in biasing engagement with said arm for normally holding said arm bly disposed in said cavity substantially in parallel relation and adjacent to said arm and extending to the outside of said body, another spring disposed in said cavity and engageable with said plunger so as to bias said plunger in the direction toward said outside position, said arm being engageable with said plunger to permit movement of said plunger in said direction only when said arm is in said contact-open position, said plunger being engageable with said arm when said plunger is moved in opposition to said other spring to then permit said arm to move to said contact-closed position, a plate member attached to said body and extending over said cavity and over said plunger and said arm, said plate member having a pivot element for said arm and having stop means engageable with said plunger for limiting the plunger movement in said direction.

11. A relay, comprising an insulating body having condition-responsive control means and having a cavity, a stationary contact means mounted on said body, a pivotally movable insulating arm disposed in said cavity and having movable contact means engageable with said stationary contact means, a spring disposed in said cavity in biasing engagement with said arm, said arm being engageable by said control means to be moved thereby in opposition to said biasing spring, a plunger slidably disposed in said cavity and extending to the ouside of said body, a wire spring disposed in said cavity having an end extending across said plunger, said plunger having axially spaced notches for selectively receiving said end to bias said plunger toward said outside and being engageable with said arm for controlling the movement of said arm when said plunger is displaced in the opposite direction, a plate member attached to said body over said cavity and extending over said plunger and said arm for securing them in proper relative positions within said cavity, said plate member having stop means engageable with said spring end to limit the displacement of said plunger.

GEORGE C. ARMSTRONG. ROBERT T. BASNETT. DELBERT ELLIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,195,012 Pierce Mar. 26, 1940 2,322,161 Schleicher June 15, 1943 2,414,513 Ellis et al Jan. 21, 1947 2,501,156 Bolesky Mar. 21, 1950 

